Suffering from bad breath. Feel mucus in throat. Is this due to sinus infection?

Hey I'm a 19 year old male. I have a problem with my breath, I mean I clean my teeth,gums,and tongue regularly but my bad breath is still there no matter how good I clean my mouth it still smells but I'm starting to think the smell is coming from my throat. Is that possible for your throat to make you have bad breath? And I also spit a lot because I feel like I have mucus in my throat ALL the time. Does that mean I have a sinus infection? And does that cause bad breath to?

Brief answer...Seems to be due to chronic sinusitis
Detailed answer...
Hello,
Thanks for the query.
The most common causes for bad breath in a person are poor dental hygiene, gum diseases like periodontal infections, use of tobacco and smoking, persistent dry mouth etc. Since you are observing proper dental hygiene and are not complaining of any gum pain or bleeding, then local mouth problems seem to be not the reason for your bad breath.
Your history of constant spitting and having constant feeling of mucus at the back of your throat suggest the problem to be either chronic sinusitis or may be acid reflux disease called as GERD.
The best would be to consult your doctor for a proper examination and necessary investigations, so that a proper diagnosis can be made out and proper treatment instituted.
Until then, do the following...
Do regular brushing twice a day along with flossing of teeth
Drink plenty of water
Avoid smoking, tobacco or betel nut, if any
I hope it helps however, you may revert to me for any further query.
Best of luck
Thanks